Anyone used 9v "memory saver" when changing Battery in 430?

Getting ready to change Batter in a Friends 2007 430....Was thinking of using those 9v memory savers you plug into the cig. lighter, to keep the memory for the Radio codes and ECU......Would I have to have ign. Switch on to keep the cig lighter current open? and Would that hurt anything? Its just 9volts.

some even plug into the OBII reader, but I kind of hate to do it that way. Any suggestions....thanks.....

I have 2008 that I may do later, We're going to "experiment on his car first"

 

I read on a Bmw forum where a guy used the OBD hook up like above , but it messed up all his warning lights and such. He said it depends on what pins get the 9 volt power. That's why I was wondering if someone actually tried it on a F car. Or if anyone has used the cig lighter to supply the 9 volt memory saver .... I hate to be the first . I know they make a memory saver that uses alligator clips to battery cables, but with the limited working space, they would probably get knocked off in the process. IDK though
Thanks though. Good to know about MB. My daughter has one too
Mark